1. The Field of the Invention
The present invention relates generally to a spinal fixation system, and more particularly, but not necessarily entirely, to a surgical device capable of immobilizing at least one vertebra of the spine, fusing a portion of the spinal column.
2. Description of Related Art
The spine is a flexible, multi-segmented column that supports the upright posture in a human while providing mobility to the axial skeleton. The lumbar spine serves the functions of encasing and protecting vital neural elements and provides structural support for the body by transmitting the weight of the body through the pelvis to the lower extremities. Because there are no ribs attached to the lumbar spine, it has a relatively wide range of motion.
The spine is made up of bone, intervertebral discs, synovial joints with their articular cartilage, synovial capsules and, as part of the back, is surrounded by supporting ligaments, muscle, fascia, blood vessels, nerves, and skin. As in other areas of the body, these elements are subject to a variety of pathological disturbances: inflammation, trauma, neoplasm, congenital anomalies, disease, etc. In fulfilling its role in the back, the spine can be subjected to significant trauma which plays a dominant role in the etiology of low back pain. Trauma frequently results in damage at the upper end of the lumbar spine, where the mobile lumbar segments join the less mobile dorsal spine. Excessive forces on the spine not only produce life-threatening traumatic injuries, but may contribute to an increased rate of degenerative change. Degenerative changes tend to develop in the lower lumbar intervertebral discs, most commonly in the third decade. Osteoarthritis produces changes in the facet joints by middle age.
Stabilization of the spine is one method used to treat trauma, tumors, disabling pain, neurological compromise, deformity or degenerative pathologies. Many methods and devices have been used to improve the stabilization of the spine, such as implantation of rods positioned parallel to the spinous process using polyaxial screws, pedicle screws or other types of bone screws, which attach a connector to the rod. Other methods have been used to accomplish stabilization of the spine. However, a recurrent problem for spinal fixation is the differing anatomy of each patient, which creates a challenge for effectively attaching the requisite instrumentation to bone of the spine.
Attempts have been made in the prior art to provide alternatives for attaching instrumentation to the spine. U.S. Pat. No. 5,613,968 (granted Mar. 25, 1997 to Lin) discloses an orthopedic fixation device using a fixation ring, a universal pad, a threaded fixation element, and a fastening nut. This device is characterized by several disadvantages, including the many individual pieces that must be attached by a surgeon prior to implantation. The device is designed such that a limited degree of movement in the bone screw may be achieved through articulation between an arcuate washer and a universal pad, which does not serve to create a locking fit.
There are several other spinal fixation devices with differing modes of attachment known in the prior art, such as that disclosed in U.S. Pat. No. 5,938,663 (granted Aug. 17, 1999 to Petreto). This patent reference discloses a spinal instrument for adjustable connecting rods comprising a nut that clamps to a receiving and locking assembly. The device has a ball joint used for angularly connecting the rod to the receiving and locking assembly, however, this device is characterized by a limited range of motion, which is not advantageous for complex anatomical situations.
U.S. Pat. No. 6,123,706 (granted Sep. 26, 2000 to Lange) discloses a support system for stabilizing the spine for surgical treatment which requires spinal fixation. The device provides for a bone screw to have a limited range of motion and utilizes a nut to fasten and lock the device. Disadvantageously, the device utilizes several component parts to create a locking mechanism to fix a bone screw at differing angles.
U.S. Pat. No. 6,187,005 (granted Feb. 13, 2001 to Brace et al.) discloses a variable angle spinal fixation system which includes a longitudinal member, a threaded fastener, and a connector member for connecting the fastener. The device is characterized by a locking system, which is disadvantageous because of the number of component parts increasing the complexity of the system, including inserting a polyaxial screw into a threaded skirt, which in turn is inserted into the connector to create a lock. Additionally, the polyaxial screw portion creates an overly large profile system which has the potential for discomfort when implanted onto a patient's spine.
The prior art is thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
It is noteworthy that none of the references in the art known to applicant provides a spinal fixation device providing a pedicle screw having a variety of attachment angles with a low profile, and a locking system utilizing a pedicle screw and a clamp forming a morse taper locking fit. There is a long felt, but unmet, need for a spinal fixation device that has a low profile, is easily assembled, is relatively inexpensive to make, and simple in operation.
The prior references in the art relating to spinal fixation devices utilize various mechanical features for enabling the surgeon to selectively adjust the alignment of the patient's spine and then to secure that alignment with the locking of the spinal fixation device to the spine. Most of these devices are relatively difficult to adjust and require undue surgical time in their implantation. Further, due to the wide variation in spinal dimensions and availability of suitable attachment sites, most devices have limited application. Further still, these devices do not allow the surgeon to easily manipulate and position the bone screws prior to final tightening of the device.
In view of the foregoing, it would be a significant advancement in the art to provide a spinal fixation apparatus and method that was highly modular and interchangeable, simplified, and would increase the ease of installation and adjustment while decreasing the total time required for surgical implantation and fixation. Such a novel spinal fixation apparatus and method is disclosed and claimed herein.